1. Field of the Invention
The present invention relates to a semiconductor device and a method for forming the same. More particularly, the present invention relates to a semiconductor device having contact holes of differing depths and a method for forming the contact holes simultaneously.
2. Description of the Related Art
Electronic products such as computers, mobile phones, multimedia players, digital cameras, etc., may include semiconductor devices such as a memory chip for storing information and a processing chip for controlling information. The semiconductor devices may include electronic elements such as a transistor, a resistor, a capacitor, etc. Electronic elements may be integrated on a semiconductor substrate, and there may be a demand for a high level of integration in order to provide the high performance and reasonable price that consumers have come to demand.
In order to achieve high levels of integration, advanced processing technologies such as a photolithography process may be required in the manufacturing process for the semiconductor device. However, advanced processing technologies may be immensely expensive and time consuming to develop, thus limiting advances in the degree of integration.
Recently, advances have been made in increasing the level of integration by forming semiconductor devices having a plurality of stacked layers, which may necessitate the formation of contact plugs of differing heights in a single device. For example, flash memory devices having multi-layer transistors have been developed in order to provide a high degree of integration. A typical method for forming such a flash memory device may include a process of forming contact plugs having respectively different heights. In particular, to form the contact plugs having respectively different heights, contact holes having respectively different depths may be formed.
If contact holes having different depths are simultaneously formed through one etching process, etching damage may occur in a thin layer at the bottom of one of the contact holes, i.e., at the bottom of the less-deep contact hole. Such etching damage may reduce the reliability and the operational characteristics of the device. On the other hand, if the contact holes are formed separately, the number of processes increases, which may lower productivity and/or product yield.